The present invention relates to an exhaust gas purification device for an internal combustion engine. Specifically, it relates to art for trapping and removing PM (particulate matter) contained in exhaust gas of a diesel engine 2. Description of the Related Art
In a diesel engine, in order to trap and remove PM containing carbon as a main component contained in exhaust gas, DPF (diesel particulate filter) has been widely used as an exhaust gas purification device. In such DPF, when PM deposits, a trapping function decreases and also pressure loss increases. Consequently, a catalyst to promote the oxidation action of PM is supported on DPF and PM is oxidized (burned) and discharge in the form of carbon dioxide to remove PM, thereby DPF being regenerated. As the catalyst for use in PDF, platinum has been widely adopted. Also, in order to achieve a stable oxidation reaction, it is common to add an oxygen storage material such as ceria or zirconia to the catalyst.
However, recently, since the price of platinum rises steeply, a material that may be substituted for platinum has been investigated as one countermeasure. For example, an oxygen ion conductive material such as a perovskite type oxide has been proposed (refer to JP-A-2007-224747).
However, the oxygen ion conductive material as stated above is poor in oxidation performance as compared with platinum and particularly at a high temperature region, there is a risk that carbon monoxide may be generated as a result of insufficient oxidation of PM.